Various types of amplifiers are used in a variety of applications such as audio applications. For example, as mobile phone technology progresses, increasingly sophisticated, efficient amplifiers that produce high-fidelity sound are incorporated into mobile phones. Some types of amplifiers provide high-fidelity sound, but they use power inefficiently. Other types of amplifiers use power efficiently, but produce poor sound quality. Combinations of these types of amplifiers produce high-fidelity sound and use power efficiently, but they are difficult to design. Thus, improvements in amplifier technology are desirable.